Communication devices such as wireless devices are also known as, e.g., User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system, wireless communications network, or cellular network. The communication may be performed, e.g., between two wireless devices, between a wireless device and a regular telephone, and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, tablets or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The wireless communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g., a Radio Base Station (RBS), which sometimes may be referred to as, e.g., “Evolved Node B (eNB)”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Half Duplex Operation
In Half Duplex (HD), or more specifically in Half Duplex Frequency Division Duplex (HD-FDD), the UL and DL transmissions take place on different paired carrier frequencies, but not simultaneously in time, in the same cell. This means the UL and DL transmissions take place in different time resources. Examples of time resource are symbol, time slot, subframe, Transmission Time Interval (TTI), interleaving time etc. . . . . In other words, UL and DL, e.g., subframes, do not overlap in time. The number and location of subframes used for DL, UL or unused subframes may vary on the basis of frame or multiple frames. For example, in one radio frame, e.g., frame #1, subframes #9, #0, #4 and #5 may be used for DL and subframes #2 and #7 are used for UL transmission. But in another frame, e.g., frame #2, subframes #0 and #5 may be used for DL and subframes #2, #3, #5, #7 and #8 are used for UL transmission.
Machine Type Communication (MTC)
The Machine-to-Machine (M2M) communication, or aka, MTC, may be used for establishing communication between machines and between machines and humans. The communication may comprise exchange of data, signaling, measurement data, configuration information etc. . . . . The device size may vary from that of a wallet to that of a base station. The M2M devices may be often used for applications like sensing environmental conditions, e.g. temperature reading, metering or measurement, e.g., electricity usage etc . . . , fault finding or error detection etc. . . . . In these applications, the M2M devices may be active very seldom, but over a consecutive duration depending upon the type of service, e.g., about 200 milliseconds (ms) once every 2 seconds, about 500 ms every 60 minutes etc. . . . . The M2M device may also do measurements on other frequencies or other RATs.
Low-Cost MTC
It is envisaged that MTC UEs may be deployed in the future in huge numbers, large enough to create an eco-system on its own. Lowering the cost of MTC UEs may enable implementation of the concept of the “internet of things”. MTC UEs used for many applications may require low operational power consumption and are expected to communicate with infrequent small burst transmissions. Therefore, one category of M2M devices is referred to as low cost devices. For example, the cost reduction may be realized by having just a single receiver in the UE. The cost may be further reduced by having single receiver and HD-FDD capability. A low cost UE may also implement additional low cost features such as, smaller DL and UL maximum transport block size, e.g., 1000 bits, and reduced DL channel bandwidth of 1.4 MHz for data channel, e.g. Physical Downlink Shared CHannel (PDSCH). For example, a low cost UE may comprise a HD-FDD, and one or more of the following additional features: single receiver, smaller DL and/or UL maximum transport block size, e.g., 1000 bits, and reduced DL channel bandwidth of 1.4 MHz for data channel.
HD Operation of Low-Cost MTC
HD-FDD operation is a technique that may lower the cost of an MTC UE by simplifying the Radio Frequency (RF) implementation. By not requiring simultaneous transmission and reception, an HD-FDD MTC UE does not require a duplexer: in place of a duplexer a switch may be used. The eNB may still use Full Duplex FDD (FD-FDD) operation and may be required to ensure that there are no scheduling conflicts for HD-FDD MTC UEs. That is, the scheduler may ensure that a UE is not scheduled simultaneously in the DL and UL. This requirement may mean the scheduler needs to consider data and control traffic in both directions when making scheduling decisions for an MTC UE. This requirement may add to the complexity of the scheduler. For full duplex UEs, such scheduling restrictions may not be needed: this may make concurrent support of HD-FDD and FD-FDD wireless devices more complicated. When not in Discontinuous Reception (DRX), the MTC UE may continuously receive DL physical channels except when instructed by the network to transmit in the UL or when transmitting unscheduled, contention-based, Physical Random Access CHannel (PRACH). A switching time may need to be observed by HD-FDD MTC UEs when transitioning from receive to transmit and vice versa, and this, may need to be taken into account by the scheduler.
HD-FDD operation may be implemented as a scheduler constraint, implying the scheduler may ensure that a UE is not scheduled simultaneously in the DL and UL. There are occasions when simultaneous/colliding DL and UL transmissions may not be avoided by scheduler constraints, for example, when the UE transmits an unscheduled, contention-based, PRACH that may not be predicted by the eNB. It is possible that the UE may transmit a PRACH at the same time that it is scheduled via Physical Downlink Control CHannel (PDCCH)/PDSCH in the DL. In this case, the UE may not be able to receive the PDCCH/PDSCH.
The following has been further observed on UE switching times during the MTC studies:
Switching time for the DL-to-UL transition may be created by allowing the UE to DRX the last Orthogonal Frequency Division Multiplexing (OFDM) symbols in a DL subframe immediately preceding an UL subframe.
Switching time for the UL-to-DL transition may be handled by setting an appropriate amount of timing advance in the UE. Timing Advance (TA) is a mechanism that may be used to ensure that all UL transmissions from wireless devices arrive time-aligned at the network node, e.g., eNodeB. TA is a negative offset between the start of the received DL subframe and transmitted UL subframe. By adjusting the value of the offset, the transmissions from the terminals may be controlled by the eNB. This switching time may be important when the UE is close to the cell centre, with near zero timing advance. The same adjustment of the UL timing from the eNB perspective may be also applied to full duplex UEs. The eNB may decide the appropriate amount of timing advance, e.g., by defining a UE requirement on a maximum allowed switching time.
UE Measurements
Radio measurements done by the UE may be typically performed on the serving as well as on neighbor cells over some known reference symbols or pilot sequences. The measurements may be done on cells on an intra-frequency carrier, on inter-frequency carrier(s), as well as on inter-RAT carriers(s), depending upon the UE capability, whether it supports that RAT. To enable inter-frequency and inter-RAT measurements for the UE requiring gaps, the network may have to configure the measurement gaps. During the measurement gaps there is no scheduled transmission in UL or DL. Instead, the wireless device may use the gaps to perform measurements on e.g., inter-frequency or inter-RAT cells.
The measurements may be done for various purposes. Some example measurement purposes may be: mobility, positioning, Self-Organizing Network (SON), Minimization of Drive Tests (MDT), Operation and Maintenance (O&M), network planning and optimization etc. Examples of measurements in LTE are Cell identification, aka Physical Cell Identifier (PCI), acquisition, Reference Symbol Received Power (RSRP), Reference Symbol Received Quality (RSRQ), Cell Global Identification (CGI) acquisition, Reference Signal Time Difference (RSTD), UE Reception (RX)-Transmission (TX) time difference measurement, Radio Link Monitoring (RLM), which consists of Out of synchronization (out of sync) detection and in synchronization (in-sync) detection etc. Channel State Information (CSI) measurements performed by the UE may be used for scheduling, link adaptation etc. by network. Examples of CSI measurements or CSI reports are Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), Rank Indicator (RI) etc. They may be performed on reference signals like Cell Specific Reference Signal (CRS), CSI-Reference Signal (RS) or DeModulation Reference Signal (DMRS).
Radio Network Node Radio Measurements
In order to support different functions such as mobility, e.g., cell selection, handover etc., positioning a UE, link adaption, scheduling, load balancing, admission control, interference management, interference mitigation etc., the radio network node, e.g., base station, access point, relay, eNode B, may also perform radio measurements on signals transmitted and/or received by the radio network node. Examples of such measurements are Signal-to-Noise Ratio (SNR), Signal to Interference plus Noise Ratio (SINR), received interference power (RIP), Block Error Rate (BLER), propagation delay between UE and itself, transmit carrier power, transmit power of specific signals, e.g., Tx power of reference signals, positioning measurements like Timing Advance (TA), eNode B Rx-Tx time difference etc.
In existing methods, a UE may have to perform radio measurements, e.g., RSRP, RSRQ, UE Rx-Tx time difference etc . . . , on one or more cells during DL and/or UL subframes, depending upon the type of measurement. A FD-FDD UE may have full freedom to choose any DL and/or UL subframes which contain the appropriate reference signals, e.g., Primary Synchronization Signals (PSS)/Secondary Synchronization Signal (SSS), CRS, Positioning Reference Signals (PRS), Sounding Reference Signals (SRS) etc. . . . for doing the desired measurement. But a HD-FDD UE may not freely choose any subframe for performing such radio measurements. Instead, for a HD-FDD capable UE, the serving node of the UE may have to ensure that at least certain number of DL and UL subframes is available every N frames, where N≥1, at the UE for doing measurements. The switching from DL to UL, or from UL to DL, aka transition, may result in that the UE operating in HD-FDD mode is not able to receive some signals or channels in subframe/s falling between successive UL and DL subframes. Such subframes are unused by that HD-FDD UE. Typically, several HD-FDD UEs may require similar subframes for measurements, e.g., DL subframes 0 and 5, which contain PSS/SSS. This means unused subframes may be common for several HD-FDD UEs in the same cell. This leads to uneven interference and different performance between different subframes, e.g., unused subframes and subframes used for measurements. This may lead to significant performance degradation in certain subframes. In the existing methods, there is no systematic mechanism to ensure even distribution of different types of UEs across different subframes within a radio frame.
There are a number of constraints that the serving node of the UE, e.g., the scheduler, faces when assigning resources for HD-FDD UEs. As stated earlier, DL cell measurements, e.g., RSRP, RSRQ, may require a certain number of subframes. For FD-FDD UEs, this is not a problem since UL and DL may take place anytime simultaneously. However, this may be a constraint for HD-FDD UEs as the UE has to switch between UL and DL, and because of the unused subframe resulting from every switch. Therefore, the eNB scheduler may have to ensure that at least a certain number of DL and UL frames are available at the UE for doing measurements. This is a constraint in the scheduler because of the wasted subframe for every switch, or the switching time.
For HD-FDD UEs, in comparison to FD-FDD UEs, the same measurement period and sampling rate may not be sufficient because there may be more subframe constraints. This is exemplified in Table 1, wherein it is assumed that subframe 0 and 5 are reserved for cell identification data, and the UE receives a PDSCH transmission on subframe 3 and 4. This may require that the UE sends HARQ feedback in subframe 7 and 8. According to HARQ requirements in 3GPP TS 36.213 V12.1.0, ‘Physical layer procedures (Release 12)’, the UE may be required to provide HARQ feedback with a 4 subframe delay from point of reception, and the same requirement may also be valid for uplink transmission. This means that the eNB scheduler may have to reserve subframe 7 and 8 for UL. This adds a new constraint to HD-FDD UEs in addition to the switching-subframe constraint as described earlier, because for every transmission of data on DL, there may have to be a feedback on UL 4 subframe later. This means that the eNB scheduler may have to reserve subframe 6 and 9 to switch from DL to UL, and from UL to DL, respectively. In the table, the Broadcast CHannel is indicated as BCH. The Physical Hybrid ARQ Indicator CHannel is indicated as PHICH. In the particular example shown in this table, the PHICH has been received in subframes #1 and #2, as a matter of example, which are therefore, DL. A System Information Block is indicated as SIB. The Physical Uplink Control CHannel is indicated as PUCCH. The Physical Uplink Shared CHannel is indicated as PUSCH. The switching subframes are indicated as Guard Period (GP).
TABLE 1HD-FDD HARQ feedback example#0 (DL)#1 (DL)#2 (DL)#3 (DL)#4 (DL)#5 (DL)#6 (GP)#7 (UL)#8 (UL)#9 (GP)PSSPHICHPHICHPDSCHPDSCHPSSDL−>ULPUCCHPUCCHUL−>DLSSSSSSPUSCHPUSCHBCHSIB
According to the requirement in 3GPP TS 36.133, ‘Requirements for support of radio resource management (Release 12)’, a UE may, in every radio frame, assess the radio link quality, evaluated over the previous time period, against thresholds, Qout and Qin. This is normal operation for FD-FDD UEs; however, for HD-FDD UEs, which switch between DL and UL, this may become challenging. Therefore, it may be necessary for eNBs to ensure that at least certain DL subframes of the measured cell, e.g., PCell, are available for HD-FDD UEs for measuring on the CRS for radio link monitoring purposes.
As mentioned earlier, existing methods lead to uneven interference and different performance between different subframes, e.g., unused subframes and subframes used for measurements, due to uneven distribution of different types of UEs across different subframes within a radio frame. This may lead to significant performance degradation in certain subframes. Additionally, existing methods may result in interrupted communications due to scheduling conflicts with the constraints of HD-FDD wireless devices.